Oxidative skeleton breaking in epoxy–amine networks

Abstract

SynopsisThe photo and thermal oxidation of various epoxide-amine tridimensional polycondensates is studied by IR spectrophotometry and DSC. The network degradation results in a decrease of the glass transition temperature (TJ, which is correlated with the quantity of amide groups formed. For each system, the relative yield in skeleton breaks increases with the intensity of internal stresses. A mechanism involving the fl scission of a amino alkoxy macroradicals resulting from oxidation of constrained segments of the network is proposed.

Thermo-oxidative aging of epoxy coating systems

“…In PAA segments, the most reactive site is, no doubt, the ␣ amido nitrogen [23] which is expected to give mainly imides and aldehydes (Fig. 8).…”

Model-based analysis of photoinitiated coating degradation under artificial exposure conditions

“…Such a reduction is necessary to avoid a prohibitive complexity of the overall mathematical model and can be justified if all relevant experimental observations can be described by the model. Based on the detailed studies of Bellenger, Verdu, and co-workers, [28][29][30][31][32][33] the following reduced mechanism can be proposed…”

“…• Potential skeleton breaking reactions, due to internal stress, as described by Bellenger and Verdu,29 are neglected.…”

“…29,31,32 Quantum yield can be a function of moisture content, coating thickness, and many other parameters, 19,48 but that complexity is not included in the model.…”

“…According to Bellenger and Verdu 29 such a scission reaction should lead to formation of aldehyde groups, which have not been observed by Rezig et al 13 Relaxation phenomena were also neglected because the coatings were all allowed to cure at ambient conditions (see Croll et al 43 for more on this issue). The porosity of the coating, at a given position in the oxidation zone, is assumed to be a function of the fraction of crosslinks that have been broken by reaction (1).…”